The Growth and Characterization of 2D Van Der Waals Crystals by Molecular Beam Epitaxy

As metal–oxide–semiconductor field-effect transistor (MOSFET) scaling pushes to the limits of Moore’s Law, future improvements in transistor performance will require new materials or novel device structures. Low-dimensional materials, such as two-dimensional (2D) materials, offer new pathways in device scaling and design. 2D materials are atomically thin, self-terminating planar sheets of atoms that represent the limit in material thinning. For this reason, 2D materials are of interest for the continued scaling of transistors. They also show promise for use in new device technologies such as the tunnel field effect transistor and various spintronic devices.

A significant hurdle to the widespread integration of 2D materials into commercial technologies is achieving controlled and scalable synthesis methods. Despite the intense research focus on layered van der Waals crystals over the last two decades, challenges in controlling nucleation density, stoichiometry, and effective doping of 2D materials remain. In this thesis, we use molecular beam epitaxy (MBE) to investigate the growth of various 2D materials, including semiconducting WSe2, metallic Nb1+xSe2, and the topological insulator Bi2Se3. Despite their similar layered structures, the growth of each of these materials pose their own unique engineering challenges. We use a combination of in-situ and ex-situ characterization techniques to explore the processing-structure-properties relationship as it applies to the synthesis of these 2D systems.